A software bug, or defect, is the common term used to describe an error, flaw, mistake, failure or fault in a computer program or system that produces an incorrect or unexpected result or causes it to behave in unintended ways. Most bugs arise from mistakes and errors made by people in either a program's source code or its design. Others may be caused by compilers producing incorrect code.
Bugs can have a wide variety of effects with varying levels of inconvenience to the user of the program. Some bugs have only a subtle effect on the program's functionality and may thus lie undetected for long time while more serious bugs may cause the program to crash or freeze. Other bugs may have more serious ramifications such as security bugs that might for example enable a malicious user to By-pass access controls in order to obtain unauthorized privileges.
The risk (likelihood of occurrence and impact) of software bugs is immense. Virtually every business in the United States and across the globe depends on software for the development, production, distribution and support of products and services. Entire industries alone have been enabled by low-cost computational capabilities supplied by computers and software.
According to market researcher DataMonitor, the size of the worldwide software industry in 2008 was U.S.$ 303.8 billion, an increase of 6.5% compared to 2007. Americas account for 42.6% of the global software market's value. DataMonitor forecasts that in 2013, the global software market will have a value of US$ 457 billion, an increase of 50.5% since 2008.
In 2002, a study commissioned by the US Department of Commerce's National Institute of Standards and Technology concluded that software bugs, or errors, are so prevalent and so detrimental that they cost the US economy an estimated $59 billion annually, or about 0.6 percent of the gross domestic product. The Department also concluded that at the national level over half the costs of software bugs are borne by software users and the remainder by the software developers/vendors. The study also found that, although all errors cannot be removed, more than a third of these costs, or an estimated $22.2 billion, could be eliminated by an improved testing infrastructure that enables earlier and more effective identification and removal of software defects.
A number of inventions have been established that attempt to improve the quality of software. Many of these prescribe techniques for identifying defects earlier in the development cycle, automating the bug, or defect, identification process or planning through predicting modeling. However these approaches focus purely on the planning, management and prevention of software defects. They fail, however, to address the potentially more important issue of how to adequately address defects once they have been identified.